a) Field of the Invention
The present invention is directed to the manufacture and use of headphones, in particular, closed head phones.
b) Description of the Related Art
Headphones of various designs and types of construction, in particular also closed headphones, have been known for a long time.
Headphones of the type mentioned above should have the desired frequency response in all frequency positions and, in particular, this frequency response should be as linear and uniform as possible in the lower frequency range in order to allow good transmission in low frequencies as well.
For damping fundamental resonance, it is known from DE 11 35 045 to adjust a flow resistance in the acoustic baffle between the rear volume and front volume, so that the desired frequency response is achieved. This reference also discloses that outlets are provided at the rear volume which open into free space, while other outlets are provided which extend from the rear volume into the front volume via the acoustic baffle.
However, as can be gathered from the above-cited reference, each of the passages between the rear volume and front volume is provided with an acoustic flow resistance which is designed in such a way that the transducer system adopts the desired natural resonance or damping of this resonance.
In known transducer systems, the natural resonance of the electrodynamic transducer is damped by a body functioning as a flow resistance. Often, this body is coupled to the oscillating diaphragm and provides for a very small air volume between the oscillating diaphragm and the suspension or surround of the diaphragm (in a dynamic transducer with outer surround). Known bodies for forming the flow resistance comprise a partially permeable material which is rather flat in proportion to its extension in the plane. An example of a construction of a body of this kind which forms a flow resistance is also described in German Patent Application DE 197 37 461. In this case, the damping means comprise a sintered material and accordingly form a three-dimensional structure.
The volume between the diaphragm and the damping means usually has a diameter no larger than the moving diaphragm, and the height of the volume between the diaphragm and damping means is usually in the range of about 0.1 mm to 5 mm, preferably 0.2 mm to 4 mm. Closed headphones have a volume in front of the diaphragm—the front volume—which is defined by the ear, the ear cushion of the headphones and the acoustic baffle. Further, headphones of this type have a rear volume which is divided from the front volume by the diaphragm and the acoustic baffle and which, for the rest, is defined by the headphone ear shell and the acoustic baffle.
Finally, the rear volume also has the openings, already described above, according to Pat. DE 11 35 045.
In order to adjust the low-frequency component of the sound to be reproduced correctly in relation to the high-frequency component, a flow resistance is built into the acoustic baffle. As this resistance decreases, the reproduction of lower frequencies becomes softer or fainter in relation to high frequencies.